Galvanic signal path isolation in an encapsulated package using a photonic structure

ABSTRACT

An encapsulated package is provided that includes a pair integrated circuit (IC) die. A radio frequency (RF) circuit on one of the IC die is operable to transmit an RF signal having a selected frequency. An RF circuit on the other IC die is operable to receive the RF signal Encapsulation material encapsulates the IC die. A photonic waveguide couples between the RF transmitter and RF receiver to form galvanic path isolation between the two IC die. The photonic waveguide is formed by a photonic structure within the encapsulation material.

FIELD OF THE DISCLOSURE

This disclosure relates to an integrated circuit package that includes aphotonic structure in the package encapsulation material.

BACKGROUND OF THE DISCLOSURE

Individual discrete components are typically fabricated on a siliconwafer before being cut into separate semiconductor die and assembled ina package. The package provides protection against impact and corrosion,holds the contact pins or leads which are used to connect from externalcircuits to the device, and dissipates heat produced in the device.

Wire bonds may be used to make electrical connections between anintegrated circuit and the leads of the package with fine wiresconnected from the package leads and bonded to conductive pads on thesemiconductor die. The leads external to the package may be soldered toa printed circuit board. Modern surface mount devices eliminate the needfor drilled holes through circuit boards and have short metal leads orpads on the package that can be secured by reflow soldering.

Many devices are encapsulated with an epoxy plastic that providesadequate protection of the semiconductor devices and mechanical strengthto support the leads and handling of the package. Some integratedcircuits have no-lead packages such as quad-flat no-leads (QFN) anddual-flat no-leads (DFN) devices that physically and electrically coupleintegrated circuits to printed circuit boards. Flat no-lead devices,also known as micro leadframe (MLF) and small outline no-leads (SON)devices, are based on a surface-mount technology that connectsintegrated circuits to the surfaces of printed circuit boards withoutthrough-holes in the printed circuit boards. Perimeter lands on thepackage provide electrical coupling to the printed circuit board.

A dielectric is an electrical insulator that can be polarized by anapplied electric field. When a dielectric is placed in an electricfield, electric charges do not flow through the material as they do in aconductor, but only slightly shift from their average equilibriumpositions causing dielectric polarization. Because of dielectricpolarization, positive charges are displaced toward the field andnegative charges shift in the opposite direction. This creates aninternal electric field which reduces the overall field within thedielectric itself. If a dielectric is composed of weakly bondedmolecules, those molecules not only become polarized, but also reorientso that their symmetry axis aligns to the field. While the term“insulator” implies low electrical conduction, “dielectric” is typicallyused to describe materials with a high polarizability which is expressedby a number called the relative permittivity (εr). The term insulator isgenerally used to indicate electrical obstruction while the termdielectric is used to indicate the energy storing capacity of thematerial by means of polarization.

Permittivity is a material property that expresses the force between twopoint charges in the material. Relative permittivity is the factor bywhich the electric field between the charges is decreased or increasedrelative to vacuum. Relative permittivity is also commonly known asdielectric constant.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the disclosure will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is an example encapsulated package that includes a high voltagegalvanic path isolation structure formed by a photonic bandgapstructure;

FIGS. 2A-2C is a frequency dispersion plot illustrating a band gap in aphotonic bandgap structure having a hexagonal lattice;

FIG. 3 is an example of another photonic bandgap structure having asquare lattice;

FIG. 4 is a plot illustrating a portion of the electromagnetic frequencyspectrum vs. wavelength;

FIG. 5 illustrates a simulation of an example photonic waveguide formedby a photonic bandgap structure;

FIG. 6 is a cross section of an example encapsulated package thatincludes another example of a photonic waveguide formed by a multilayerphotonic bandgap structure;

FIG. 7 is a top view of an example leadframe;

FIGS. 8A-8C illustrate formation of a photonic bandgap structure usingan additive manufacture process to encapsulate an IC;

FIG. 9 illustrates a top view of an example encapsulated packagecontaining a photonic structure;

FIG. 10 is a flow chart illustrating an example process for formation ofa photonic waveguide from an photonic bandgap structure within anencapsulated package;

FIG. 11 illustrates a simulation of another example photonic waveguide;and

FIG. 12 is a cross sectional view of another example encapsulatedpackage that includes a photonic waveguide formed by a resonantstructure.

Other features of the present embodiments will be apparent from theaccompanying drawings and from the detailed description that follows.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

Specific embodiments of the disclosure will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency. In thefollowing detailed description of embodiments of the disclosure,numerous specific details are set forth in order to provide a morethorough understanding of the disclosure. However, it will be apparentto one of ordinary skill in the art that the disclosure may be practicedwithout these specific details. In other instances, well-known featureshave not been described in detail to avoid unnecessarily complicatingthe description.

The epoxy encapsulant for semiconductor chips/packages has typicallyserved the primary purpose of providing environmental and mechanicalprotection for the integrated circuit (IC). Previously, in order for anadditional package function to be added, it must be added before orafter the encapsulation step. Performing additional packaging steps mayincrease cost and limit functionality on the processes that can beperformed. A method for encapsulating an IC will now be disclosed inwhich a structure to perform an additional package function may becreated during the process of encapsulation.

As frequencies in electronic components and systems increase, thewavelength decreases in a corresponding manner. For example, manycomputer processors now operate in the gigahertz realm. As operatingfrequencies increase to sub-terahertz, the wavelengths become shortenough that signal lines that exceed a short distance may act as anantenna and signal radiation may occur. For example, in a material witha low dielectric constant of 3, such as a printed circuit board, a 100GHz signal will have a wavelength of approximately 1.7 mm. Thus, asignal line that is only 1.7 mm in length may act as a full wave antennaand radiate a significant percentage of the signal energy.

In physics, a photon represents an energy packet, or “quanta” ofelectromagnetic waves. A photon is massless, has no electric charge, andis a stable particle. In the momentum representation of the photon, aphoton may be described by its wave vector which determines itswavelength and direction of propagation.

Additive manufacturing has enabled the deposition of patterned materialsin a rapid and cost efficient manner. By utilizing additivemanufacturing, control structures may be integrated directly into theencapsulation material of an IC. As will be disclosed herein, awaveguide to allow galvanic signal path isolation may be provided in theencapsulation of an IC package through the implementation ofmulti-material photonic bandgap (PBG) structures within theencapsulation. Galvanic path isolation allows signals to be transferredbetween systems that are operating on different ground references and/ordifferent voltage levels.

Known galvanic isolation devices often use optical devices to provideisolation; however, such optical devices may be expensive.

FIG. 1 is an example encapsulated integrated circuit (IC) package 100that includes a waveguide 140 formed by a photonic bandgap structurewithin the encapsulant material 110. Waveguide region 140 will bereferred to herein as a “photonic waveguide.” A signal 141 may belaunched into photonic waveguide 140 by a transmitter structure 142 thatis formed on IC die 102 using known or later developed techniques.Photonic waveguide 140 may then conduct signal 141 to a receiverstructure 145 that is formed on IC die 103 using known or laterdeveloped techniques with minimal radiation loss. In this manner,galvanic isolation between two different systems operating on differentground references and/or voltage levels may be provided.

The general analysis and configuration of photonic waveguide 140 may bedone in a similar manner as a dielectric waveguide. For example,photonic waveguide 140 may have a rectangular cross-section. The longside of this cross-section may be twice as long as its short side, forexample. This is useful for carrying electromagnetic waves that arehorizontally or vertically polarized. For sub-terahertz signals, such asin the range of 130-150 gigahertz, a photonic waveguide dimension ofapproximately 0.5 mm×1.0 mm works well.

Waves in open space propagate in all directions, as spherical waves. Inthis way they lose their power proportionally to the square of thedistance; that is, at a distance R from the source, the power is thesource power divided by R2. Photonic waveguide 140 confines the wave topropagation in one dimension, so that under ideal conditions the waveloses no power while propagating.

IC die 102 may be attached to a die attach pad (DAP) 104 of a leadframethat includes a set of contacts 105. DAP 104 may also be referred to asa “thermal pad.” IC die 102 may also be referred to as a “chip.” IC die102 may be fabricated using known or later developed semiconductorprocessing techniques. IC die 102 may include an epitaxial (epi) layeron the top surface in which are formed various semiconductor transistordevices and interconnects. One or more conductive layers may be formedon the epi layer and patterned into interconnect traces and bond pads. Aset of bond wires 106 may be attached to contacts 105 and bond padslocated on the surface of IC die 106 using known or later developed wirebonding techniques.

Similarly, IC die 103 may be attached to a die attach pad 107 of theleadframe that includes a set of contacts 108. IC die 103 may befabricated using known or later developed semiconductor processingtechniques. IC die 103 may include an epitaxial (epi) layer on the topsurface in which are formed various semiconductor transistor devices andinterconnects. One or more conductive layers may be formed on the epilayer and patterned into interconnect traces and bond pads. A set ofbond wires 109 may be attached to contacts 108 and bond pads located onthe surface of IC die 103 using known or later developed wire bondingtechniques.

Encapsulated package 100 forms two galvanic path isolated regions 111,112. In region 111, DAP 104 and IC die 102 are galvanically isolatedfrom DAP 107 and IC die 103 in region 112. Region 111 may be coupled toanother device or system that is operating on a different groundreference and/or at a different voltage reference than region 112. Inthis manner, a signal from a device or system may be coupled to contacts105 and provided thereby to transmitter circuitry on IC die 102,converted to an RF signal, and launched into photonic waveguide 140. Thephotonic signal may then be received by receiving circuitry on IC die103, converted back to an electrical signal, and provided to anotherdevice or system via contacts 108.

Components in region 111 are separated from components in region 112 bya separation distance that forms voltage barrier region 113. The voltagebreakdown strength of the encapsulation material in this region and theseparation distance must be sufficient to prevent voltage breakdownbetween region 111 and region 112. The PBG structure formed by nodes 121and lattice material 123 may provide more voltage protection than asingle dielectric material since two or more different types of materialmay be used to form the nodes 121 and the lattice 123. Voltage isolationof 10 kvolts or more may be provided in this manner by appropriateselection of encapsulation materials 110, 121, 123 and physicalseparation distance between DAP 104 and DAP 107 and/or IC 102 and IC103. A required separation distance for a target voltage breakdownstrength with a given selection of encapsulation material may bereferred to herein as a “voltage breakdown distance.”

In this example, encapsulated package 100 is a dual-flat no-leads (DFN)package; however, in other embodiments various known or later developedpackaging configurations, such as DFN, MLF, SON, flip chips, dual inlinepackages (DIP), etc, may be fabricated using the techniques disclosedherein to form an encapsulated package with a photonic bandgap structureincluded within the encapsulant material.

In this example, a solid encapsulant material 110 surrounds andencapsulates IC die 102 and IC die 103. A portion of the encapsulationmaterial may include a matrix of interstitial nodes such as indicated at121 that may be filled with a material that is different fromencapsulation material 110. In this example, nodes 121 are arranged in athree dimensional array of spherical spaces that are in turn separatedby a lattice of encapsulation material 123. Encapsulation material 123may be the same or different as solid encapsulation material 110. Thestructure formed by the matrix of nodes 121 and lattice 123 will bereferred to herein as a “photonic bandgap structure.” The photonicbandgap (PBG) structure formed by periodic nodes 121 may effectivelyguide electromagnetic signal 141 through photonic waveguide 140.

Solid encapsulant material 110 is typically an epoxy based material thatprovides mechanical protection and seals IC die 102 from environmentalgases and liquids.

As mentioned above, lattice 123 may be formed from the same material assolid encapsulation material 110, or it may be formed using a differentmaterial by using an additive manufacturing process. The array of nodes121 may be formed with one or more different materials. For example,some of the nodes, such as nodes 121, may be filled with a firstmaterial and some of the nodes 121 may be filled with different types ofmaterial. There may be a number (N) of different materials that are usedto fill N different sets of nodes within encapsulation material 123.Node material may be a polymer or other material that has differentintrinsic material properties from the lattice material 123. Forexample, the node material may have various different intrinsic materialproperties from the lattice material, such as permittivity,permeability, conductivity, etc.

For example, certain nodes 121 may be filled with a high dielectricmaterial, while other nodes 121 are filled with a low dielectricmaterial. In some embodiments, node material 121 may be air, some othergas, or even a vacuum.

In the example of FIG. 1, lattice 123 forms a square three dimensional(3D) array of spherical nodes. In other embodiments, a differentlyshaped lattice may be formed to produce other shapes of arrays and nodes121, such as: triangular, rectilinear, hexagonal, round nodes, elongatednodes, tubes, etc.

In some embodiments, die attachment 125 may be a thin layer of adhesivematerial. In other embodiments, die attachment 125 may include a portion126 that is also a photonic bandgap structure.

A photonic crystal is an artificially manufactured structure, ormaterial, with periodic constitutive or geometric properties that aredesigned to influence the characteristics of electromagnetic wavepropagation. When engineering these crystals, it is possible to isolatethese waves within a certain frequency range. Conversely it may be morehelpful to consider these waves as particles and rely on thewave-particle duality throughout the explanation. For this reason,reference to “propagation” herein may refer to either the wave orparticle movement through the substrate. Propagation within thisselected frequency range, referred to as the band gap, is attenuated bya mechanism of interferences within the periodic system. Such behavioris similar to that of a more widely known nanostructure that is used insemiconductor applications, a photonic crystal. The general propertiesand characteristics of phononic and photonic structures are known, forexample, see: “Fundamental Properties of Phononic Crystal,” Yan Pennecand Bahram Djarari-Rouhani, Chapter 2 of “Phononic Crystals,Fundamentals and Applications” 2015, which is incorporated by referenceherein.

Photonic crystals may be formed by a periodic repetition of inclusionsin a matrix. The dielectric properties, shape, and arrangement of thescatterers may strongly modify the propagation of the electromagneticwaves in the structure. The photonic band structure and dispersioncurves can then be tailored with appropriate choices of materials,crystal lattices, and topology of inclusions.

Similarly to any periodic structure, the propagation of electromagneticwaves in a photonic crystal is governed by the Bloch or Floquet theoremfrom which one can derive the band structure in the correspondingBrillouin zone. The periodicity of the structures, that defines theBrillouin zone, may be in one (1D), two (2D), or three dimensions (3D).

The general mechanism for the opening of a band gap is based on thedestructive interference of the scattered waves by the inclusions. Thisnecessitates a high contrast between the properties of the materials. Inperiodic structures, this is called the Bragg mechanism and the firstband gap generally occurs at a frequency which is about a fraction ofc/a, where “c” is a typical velocity of light, and “a” is the period ofthe structure.

Photonic bandgap structures may be designed and modeled using simulationsoftware available from various vendors. For example, physics-basedsystems may be modeled and simulated using COMSOL Multiphysics®simulation software from COMSOL®. “Multiphysics” and “COMSOL” areregistered trademarks of COMSOL AB. HFSS (High Frequency StructureSimulator) is available from Ansys. CST (Computer Simulation Technology)offers several simulation packages.

Various configurations of dielectric waveguides (DWG) and signallaunching techniques are described in U.S. Pat. No. 9,306,263, entitled“Interface Between an Integrated Circuit and a Dielectric WaveguideUsing a Dipole Antenna and Reflector” and is incorporated by referenceherein.

FIG. 2A is a frequency dispersion plot illustrating a band gap in aphotonic bandgap structure having a hexagonal lattice. FIG. 2Billustrates a single cell 230 of the hexagonal matrix and illustratesBrillouin zone 231 for the hexagonal cell. FIG. 2C illustrates a largerportion of a hexagonal photonic crystal 232 formed by a 3D matrix ofnodes as indicated at 233. FIG. 3 is an example of another photonicbandgap structure having a square lattice.

The x-axis of FIG. 2A represents the periphery of Brillouin zone 231 ofphotonic crystal 232 as defined by points Γ, M, and K. The y-axisrepresents the angular frequency of acoustic energy propagating inphotonic crystal 232 in units of ωα/2πC. The various plot linesrepresent propagation paths through Brillouin zone 231. Region 235represents a photonic band gap in which the propagation of waves fallingwithin the defined band of frequencies is blocked by interferenceproduced by the crystal lattice.

The width and the frequency range covered by a photonic bandgap dependson the periodic spacing of the nodes 233, which may be represented bylattice constant “a” as indicated at 336 in FIG. 3, and the relativedifference between the dielectric constant of the lattice material andthe dielectric constant of the nodes. For example, the frequency rangecovered by photonic bandgap 235 may be shifted to a higher frequencyrange for larger relative differences between the dielectric constant ofthe lattice and the dielectric constant of the nodes, while the photonicbandgap 235 may be shifted to a lower frequency range for smallerrelative differences between the dielectric constant of the lattice andthe dielectric constant of the nodes.

FIG. 4 is a plot illustrating a portion of the electromagnetic frequencyspectrum vs. wavelength for an example dielectric solid material. Thevelocity (v) of an electromagnetic wave in a vacuum is approximatelyequal to the speed of light (c) in a vacuum, which is approximately3×10⁸ m/s. The velocity of an electromagnetic wave through a solidmaterial is defined by expression (1), where ε_(r) is the relativepermittivity of the solid material, which may also be referred to as the“dielectric constant” of the materialv=c/√{square root over (εr)}  (1)

The photonic wavelength (λ) may be determined using expression (2),where the velocity (v) in dielectric materials is typically on the orderof 1-2.5×10⁸ m/s for dielectric constant values in the range ofapproximately 1-10, and f is the frequency of the photon.lambda(λ)=v/f  (2)

For electromagnetic signals in the GHz to low THz frequency range, forexample, the corresponding wavelengths in encapsulant material 120 maybe in the range of several microns to several hundred microns, asindicated at 400. The opening of wide photonic band gaps requires twomain conditions. The first one is to have a large physical contrast,such as density and speed of propagation of the wave movements, betweenthe nodes and the lattice. The second condition is to present asufficient filling factor of the nodes in the lattice unit cell. Theforbidden band gap occurs in a frequency domain given by the ratio of aneffective propagation velocity in the composite material to the value ofthe lattice parameter of the periodic array of nodes. Referring to FIG.3, as a rule of thumb the lattice dimension 336 may be selected to beabout one half of the wavelength of the center of the target photonicbandgap.

While the effect of dielectric constant (εr) is described above, otherintrinsic properties of a material may be evaluated during the design ofa PBG structure, such as permeability, conductivity, etc.

FIG. 5 illustrates a simulation of an example photonic waveguide 540formed by an example photonic bandgap structure 550. This exampleillustrates a photonic waveguide that may be similar to photonicwaveguide 140 in IC 100, referring back to FIG. 1. As described above, aphotonic bandgap structure may be formed within encapsulation material123 by inserting a matrix of nodes 121 with a periodic spacing. In thisexample, the x-axis node spacing 554 is approximately equal to they-axis node spacing 556. The z-axis node spacing (not shown) is alsoapproximately the same as node spacing 554, 556 in this example.

The node spacing 554-556 in this example may be selected to beapproximately one half the wavelength of a selected frequency ofelectromagnetic radiation represented by photons 552 that should beguided by bandgap structure 550. In this manner, electromagnetic energyin the form of photons 552 that falls within the bandgap frequency rangeof PBG structure 550 may be guided through photonic waveguide 540 isillustrated by signal vector 541.

FIG. 6 is a cross sectional view of an example encapsulated package 600that includes several layers of bandgap material, 660, 661, 662. In thisexample, three layers are illustrated, but in other embodimentsadditional layers may be included. Each layer 660-662 may be designed tohave a different bandgap frequency range so that the combination oflayers may provide a photonic waveguide 640 that may guide a largerrange of frequencies than a single layer PBG structure.

While only a top portion and a bottom portion of multiple layers 660-662are shown in FIG. 6, it is to be understood that layers 660-662 maysurround and enclose photonic waveguide region 640 to guide photonicsignal 141 from IC 102 to IC 103.

FIG. 7 is a top view of an example QFN leadframe 700 that may be used tosupport IC 102, 103 in FIG. 1, for example. Other types of packages mayuse a leadframe strip that has a different known or later developedconfiguration. Lead frame strip 700 may include one or more arrays ofindividual lead frames. Lead frame strip 700 is typically fabricatedfrom a copper sheet that is etched or stamped to form a pattern of dieattach pads and contacts. Lead frame strip 700 may be plated with tin oranother metal that will prevent oxidation of the copper and provide alower contact surface that is easy to solder. An IC die may be attachedto each individual lead frame.

Each individual leadframe may include a pair of die attach pads, such asdie attach pads 104, 107 that are separated by a distance to providevoltage isolation. Each individual lead frame also includes a set ofcontacts that surround the die attach pads, such as contacts 105, 108. Asacrificial strip of metal connects all of the contacts together andprovides mechanical support until a sawing process removes it. An ICdie, also referred to as a “chip,” may be attached to each die attachpad during a packaging process, such as IC die 102, 107. Wire bondingmay then be performed to connect bond pads on each IC chip to respectivecontacts on the lead frame. The entire lead frame strip 700 may then becovered with a layer of mold compound using an additive process asdescribed in more detail below to encapsulate the ICs. Lead frame strip700 may then be singulated into individual packaged ICs by cutting alongcut lines 728, 729.

FIGS. 8A-8C are cross sectional views illustrating fabrication of theexample encapsulated package 100 of FIG. 1. IC die 102 may be attachedby die attach layer 842 to a die attach pad 104 of a leadframe that maybe part of a leadframe strip similar to leadframe strip 700 shown inFIG. 7 that includes a set of contacts 105. IC die 102 may be fabricatedusing known or later developed semiconductor processing techniques. ICdie 102 may include an epitaxial (epi) layer 841 on the top surface inwhich are formed various semiconductor transistor devices andinterconnects. One or more conductive layers may be formed on the epilayer and patterned into interconnect traces and bond pads 843. A set ofbond wires 106 may be attached to contacts 105 and bond pads 843 locatedon the surface of IC die 102 using known or later developed electricalconnection techniques. While not shown in FIG. 8A, IC die 103 may besimilarly constructed and attached to DAP 108. In this example, ICpackage 100 is a dual-flat no-leads (DFN) package; however, in otherembodiments various known or later developed packaging configurations,such as MLF, SON, flip chip, dual inline packages (DIP), etc, may befabricated using the techniques disclosed herein to form an encapsulatedpackage with a photonic waveguide formed within the encapsulantmaterial.

FIG. 8B is a cross sectional view illustrating partial formation ofencapsulation material 110. Additive manufacturing processes are nowbeing used in a number of areas. The International Association forTesting Materials (ASTM) has now promulgated ASTM F7292-12a “StandardTerminology for Additive Manufacturing Technologies” 2012 which isincorporated by reference herein. Currently, there are seven families ofadditive manufacturing processes according to the ASTM F2792 standard,including: vat photopolymerization, powder bed fusion, binder jetting,material jetting, sheet lamination, material extrusion, directed energydeposition. Hybrid processes may combine one or more of these sevenbasic processes with other manufacturing processes for additionalprocessing flexibility. Recent process advances allow additivemanufacturing of 3D structures that have feature resolution of less than100 nm, such as direct laser lithography, multi-photon lithograph,two-photon polymerization, etc.

In this example, a vat photopolymerization process may be used in whichleadframe strip and the ICs attached to it, such as IC die 102, arelowered into a vat of liquid photopolymer resin. A light source, such asa laser or projector, may then expose selected regions of the liquidphotopolymer resin to initiate polymerization that converts exposedareas of the liquid resin to a solid. In this manner, layers ofencapsulant material 110 may be formed in selected shapes. For example,encapsulant material that forms lattice 123 may be the same or differentas the solid encapsulant material 110. Nodes 121 may be formed with anyselected lattice spacing.

FIG. 8C is a cross sectional view illustrating further partial formationof encapsulation material 110 around IC die 102. Additional layers ofliquid encapsulation material 110 have been exposed and converted to asolid. Selective exposure of the liquid resin allows lattice 123 to beformed with nodes 121, as described with regard to FIG. 1. A smallportion of photonic waveguide 140 is illustrated in FIG. 8C. Photonicwaveguide 140 is formed in this example by omitting nodes 123 from theencapsulation material in the region that forms photonic waveguide 140.Photonic waveguide 140 is positioned to couple to transmitter launchstructure 142.

The leadframe strip may be submerged in different vats at differenttimes in order to allow different materials to form the nodes 121 withinlattice 123.

Additional layers of resin may be exposed and hardened to form the finaloutside encapsulation layer illustrated in FIG. 1. The leadframe stripmay then be sawed or otherwise separated into individual encapsulated ICpackages.

In another embodiment, other additive manufacturing processes may beused to form encapsulation material 110. For example, a powdered beddiffusion process may be used in which a powdered material isselectively consolidated by melting it together using a heat source suchas a laser or electron beam.

In another embodiment, a material jetting process may be used in whichdroplets of material are deposited layer by layer to produce a photonicwaveguide within an encapsulation structure as described herein.However, bond wires 106 may require extra care to avoid disrupting thedroplet streams.

In another embodiment, bond wires are not initially bonded to contacts105 and bond pads 843. In this example, a material jetting process maybe used in which droplets of material are deposited layer by layer toproduce a photonic bandgap structure as described herein. As part of thematerial jetting process, a conductive material may be deposited to formthe bond wires between contacts 105 and bond pads 843. In someembodiments, a sintering process may be done by heating the encapsulatedleadframe 700 assembly to further solidify the bond wires. The leadframestrip 700 may then be sawed or otherwise separated into individualencapsulated IC packages.

In another embodiment, IC die 102 is not initially attached to dieattach pad 104 of a leadframe that may be part of a leadframe stripsimilar to leadframe strip 700 shown in FIG. 7. In this example, a vatphotopolymerization process may be used in which the leadframe strip islowered into a vat of liquid photopolymer resin. A light source, such asa laser or projector, may then expose selected regions of the liquidphotopolymer resin to initiate polymerization that converts exposedareas of the liquid resin to a solid. In this manner, layers ofencapsulant material 110 may be formed in selected shapes. In thismanner, a photonic bandgap structure 126 as shown in FIG. 1 may befabricated on top of die attach pad 104 to isolate a later attached ICdie from die attach pad 104. Spaces may be left above each contact 105for later attachment of bond wires. A set of bond wires 106 may beattached to contacts 105 and bond pads 643 located on the surface of ICdie 106 using known or later developed wire bonding techniques.Additional layers of resin may be exposed and hardened to form anadditional photonic bandgap structure as described with regard to FIGS.8A-8C, for example. The leadframe strip may then be sawed or otherwiseseparated into individual encapsulated IC packages.

In another embodiment, the photonic bandgap structure may be fabricatedusing a lattice material that includes filler particles diffusedthroughout the lattice material in place of the explicitly formed nodesas described above, such as nodes 121. In this case, the fillerparticles are selected to have a size and material composition that willinfluence the characteristics of electromagnetic wave propagation, asdescribed above. The filler material may be a polymer or other materialthat has different intrinsic material properties from the latticematerial, in a similar manner as the difference between nodes 121 andlattice material 123. In some embodiments, the filler material may havea higher dielectric constant than the lattice material, while in otherembodiments the filler material may have a lower dielectric constantthan the lattice material, for example.

In another embodiment, multiple photonic bandgaps may be formed by usingtwo or more types of fillers. For example, a portion of the fillermaterial may have a high dielectric constant, while another portion ofthe filler material may have a low dielectric constant. In someembodiments, different size filler particle may be used in differentregions or in a same region to form multiple bandgaps. In someembodiments, a different number of filler particles per unit volume maybe used in different regions to form different bandgaps.

In this case, the filler dispersion may not be perfectly crystalline,but there will be a statistical mean separation of the filler particlethat may lend itself to a bandgap based on the statistical meanseparation distance of the filler particles.

An additive manufacturing process may be used to encapsulate an IC dieusing two or more different polymers, such as one with filler particlesand one without filler particles to form the PBG structures as describedherein or other configurations of PBG structures.

Alternatively, a selective molding process may be used in which one areaof the encapsulation is molded with first polymer having either nofiller particles or a first configuration of filler particles (size,material, number of particles per unit volume, etc.) and other areas aremolded with a polymer having a different filler particle configurationto form a PBG structure as described herein or other configurations ofPBG structures.

FIG. 9 is top view of an example encapsulated package 900 that includesa photonic waveguide provided by a photonic bandgap structure within theencapsulant material as described herein. IC 900 is an illustration of adual-flat no-leads (DFN) IC package that was encapsulated using additivemanufacturing process to form photonic waveguide structures within theencapsulation material as described herein. Flat no-leads packages suchas quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically andelectrically connect integrated circuits to printed circuit boards. Flatno-leads, also known as micro leadframe (MLF) and SON (small-outline noleads), is a surface-mount technology, one of several packagetechnologies that connect ICs to the surfaces of PCBs withoutthrough-holes. Flat no-lead is a near chip scale plastic encapsulationpackage made with a planar copper lead frame substrate. Perimeter landson the package bottom provide electrical connections to the PCB. The QFNpackage is similar to the quad-flat package, and a ball grid array.

DFN package 900 includes a set of contacts 905 arrayed on one side ofthe package on the bottom side and a set if contacts 908 arrayed on anopposite side. The entire assembly is encapsulated in an encapsulationmaterial 910 using a manufacturing process as described herein toprovide galvanic path isolation using a photonic waveguide photonicbandgap structure. While a DFN is illustrated in FIG. 9, otherembodiments may use other types of integrated circuit packages.

As described above in more detail, DFN package 900 may provide galvanicpath isolation between a system operating in a voltage region 911 andanother system operation in a different voltage region 912.

FIG. 10 is a flow diagram illustrating fabrication of the exampleencapsulated package of FIG. 1. In one embodiment, as described above inmore detail, a pair of IC die may be attached to separate die attachpads of a leadframe that includes a set of contacts as indicated at box1002. The IC die may be fabricated using known or later developedsemiconductor processing techniques. The IC die may include an epitaxial(epi) layer on the top surface in which are formed various semiconductortransistor devices and interconnects. One or more conductive layers maybe formed on the epi layer and patterned into interconnect traces andbond pads. A set of bond wires may be attached to the contacts and bondpads located on the surface of the IC die using known or later developedwire bonding techniques.

In another embodiment, a layer of material that includes a photonicbandgap structure may be first formed on the die attach pads of theleadframe, as indicated at 1004. The encapsulation material may beformed into a lattice with periodically spaced nodes that are filledwith a different type of material to form a photonic bandgap structure.As described above in more detail, an additive manufacturing process maybe used to create the lattice and fill the nodes in the lattice.

A pair of IC die may then be attached to the layer of PBG material, asindicated at 1006.

The pair of IC die may then be completely encapsulated by an additiveprocess to form a photonic waveguide between the pair of IC die withinthe encapsulation material as indicated at 1008. A first portion of theencapsulation material may be solid and a second portion of theencapsulation material may include nodes filled with a second materialto form a photonic bandgap structure. As described above in more detail,an additive manufacturing process may be used to create a lattice andfill the periodically spaced nodes in the lattice with a different typeof material, or with several different types of material in differentlocations. A photonic waveguide may be formed during the encapsulationprocess by simply omitting nodes from the region that forms the photonicwaveguide.

In another embodiment, the encapsulation process indicated at box 1008may be done using a selective molding process in which one area of theencapsulation is molded with first polymer having either no fillerparticles or a first configuration of filler particles (size, material,number of particles per unit volume, etc.) and other areas are moldedwith a polymer having a different filler particle configuration diffusedwithin the polymer to form a PBG structure as described herein or otherconfigurations of PBG structures.

As discussed above in more detail, various types of IC packages may beformed in this manner. For example, a dual-flat no-leads (DFN) packageis illustrated in FIG. 1. However, in other embodiments various known orlater developed packaging configurations, such as DFN, MLF, SON,flip-chips, dual inline packages (DIP), etc, may be fabricated using thetechniques disclosed herein to form an encapsulated package withgalvanic path isolation provided by a photonic waveguide included withthe encapsulant material.

FIG. 11 illustrates a simulation of another example photonic waveguide1140 formed within a photonic structure 1150. Photonic structure 1150 issimilar to photonic structure 550 as illustrated in FIG. 5 in that anarray of nodes 1121 within a lattice material 1123 form an approximatelyperiodic structure. However, in this example photonic waveguide region1140 may be populated with nodes 1122. Nodes 1122 may be the same asnodes 1121, or they may be different in intrinsic properties, shape,spacing, etc.

In this example, a continuous lattice may be provided that steers thephoton energy 1141 by curving the lattice in the direction of travel.The nodes 1122 in the “pathway” do not improve propagation but do steerit. In this manner, the space in the path of the photons may be warpedas opposed to creating a hallway for them to bounce down. This may beanalogous to a boat on a river; the river (curved lattice) is alreadyflowing in a certain direction and pulls the boat (photon) in thatdirection.

An additive process as described above in more detail with reference toFIGS. 8A-8C may be used to place the array of nodes to form the curvedlattice during encapsulation of an encapsulated package.

Nodes 1122 within photonic waveguide region 1140 may configured suchthat they do not provide a bandgap to the frequency of photonic signal1141 so that photonic signal 1141 may propagate through photonicwaveguide region 1140.

Nodes 1121 may also be configured such that they do not provide abandgap to the frequency of photonic signal 1141. However, the photonicenergy of photonic signal 1141 may be directed along photonic waveguideregion by curving the lattice of photonic structure 1150 to maintain anapproximately smooth wall of nodes 1121 along the edge of phonicwaveguide region 1140. Similarly, nodes 1122 are arranged in a curvedmanner to provide a pathway for phonons 1141. Photonic structure 1150may be referred to as a “resonant structure” that acts as a bandpassstructure as opposed to a bandgap structure.

FIG. 12 is a cross sectional view of another example encapsulatedpackage 1200 that includes a photonic waveguide 1240 formed by aresonant structure 1250. In this example, resonant structure 1250 isimplemented in a similar manner as resonant structure 1150 as shown inFIG. 11 and relies on warping the lattice structure to guide phononstream 1241 from a transmitter on IC die 102 to a receiver on IC die103.

As described above in more detail, galvanic path isolation between ICdie 102 and IC die 103 is provided by the spacing 113 between the two ICdie and the dielectric strength of encapsulant material 110 and resonantstructure 1250.

OTHER EMBODIMENTS

While the disclosure has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the disclosure will beapparent to persons skilled in the art upon reference to thisdescription. For example, in some embodiments, the lattice material mayhave a relatively low dielectric constant value and the node materialmay have relatively high dielectric constant value. In otherembodiments, the lattice material may have relatively high dielectricconstant value and the node material may have a relatively lowdielectric constant value. In some embodiments, the node material may beair, another gas, or a vacuum, for example.

While PBG structures using materials with different permittivities weredescribed herein, other embodiments may use materials having differencesin other intrinsic properties, such as permeability, conductivity,magnetic, etc.

In some embodiments, a portion of the nodes may be formed with one kindof material, while another portion of the nodes may be formed with adifferent material. Several different types of material may be used toform different sets of nodes within the photonic bandgap structure tothereby tailor the performance of the photonic bandgap structure.

In some embodiments, a portion of the nodes may be formed with onelattice constant, while another portion of the nodes may be formed witha different lattice constant. Several different lattice constants may beused to form different sets of nodes within the photonic bandgapstructure to thereby tailor the performance of the photonic bandgapstructure

The nodes may be fabricated using various materials, such as: variouspolymers such as polyurethane, polyacrylates, etc., ceramic materials,metals, gases such as natural air, nitrogen etc. In some cases, a vacuummay be left and therefore no material would be used for some latticenodes.

In some embodiments, the PBG structure may be symmetric in 3D, while inother embodiments the PBG structure may be asymmetric with differentlattice spacing in different directions.

In some embodiments, the PBG structure may have a bandgap that iseffective in all directions, while in other embodiments the PBGstructure may have a bandgap in one direction but not in anotherdirection, for example.

In another embodiment, an IC die may be partially or completelysurrounded by a photonic bandgap structure in the form of an enclosurethat surrounds the IC, such as a box shaped or spherical shapedenclosure that is formed within the encapsulation material by selectiveplacement of nodes within the encapsulation material.

Another embodiment may include packages that are entirely encased inmold compound, such as a dual inline package (DIP).

In another embodiment, the PBG structure may be made with ferroelectricor magnetic material. In this case, a field bias may be applied to thePBG structure using coils or plates located on the IC die or adjacent tothe IC die to tune the bandgap. The amount of bias may be controlled bycontrol circuitry located on the IC die, or by control circuitry that isexternal to the IC die.

Certain terms are used throughout the description and the claims torefer to particular system components. As one skilled in the art willappreciate, components in digital systems may be referred to bydifferent names and/or may be combined in ways not shown herein withoutdeparting from the described functionality. This document does notintend to distinguish between components that differ in name but notfunction. In the following discussion and in the claims, the terms“including” and “comprising” are used in an open-ended fashion, and thusshould be interpreted to mean “including, but not limited to . . . .”Also, the term “couple” and derivatives thereof are intended to mean anindirect, direct, optical, and/or wireless electrical connection. Thus,if a first device couples to a second device, that connection may bethrough a direct electrical connection, through an indirect electricalconnection via other devices and connections, through an opticalelectrical connection, and/or through a wireless electrical connection.

Although method steps may be presented and described herein in asequential fashion, one or more of the steps shown and described may beomitted, repeated, performed concurrently, and/or performed in adifferent order than the order shown in the figures and/or describedherein. Accordingly, embodiments of the disclosure should not beconsidered limited to the specific ordering of steps shown in thefigures and/or described herein.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the disclosure.

What is claimed is:
 1. A device, comprising: a first integrated circuit(IC) die having an electromagnetic transmitter circuit, theelectromagnetic transmitter circuit having an output configured to emitan electromagnetic signal; a second IC die having an electromagneticreceiver circuit, the electromagnetic receiver circuit having an inputconfigured to receive the electromagnetic signal, the second IC diespaced apart from the first IC die; a leadframe having first and seconddie attach pads, the first die attach pad separated from the second dieattach pad; a photonic structure including a photonic waveguide coupledbetween the output of the electromagnetic transmitter circuit and theinput of the electromagnetic receiver circuit, a portion of the photonicstructure being located between the first IC die and the first dieattach pad; and an encapsulation material encapsulating the first ICdie, the second IC die and the photonic waveguide.
 2. The device ofclaim 1, wherein the photonic waveguide includes a photonic bandgap(PBG) structure.
 3. The device of claim 2, wherein the PBG structure hasa bandgap that includes a frequency of the electromagnetic signal. 4.The device of claim 2, wherein the PBG structure is a multilayer PBGstructure, in which layers of the multilayer PBG structure haverespective photonic bandgaps with different frequency ranges.
 5. Thedevice of claim 4, wherein the respective photonic bandgap of at leastone of the layers of the multilayer PBG structure includes a frequencyof the electromagnetic signal.
 6. The device of claim 4, wherein a firstlayer of the multilayer PBG structure includes a first matrix ofperiodically spaced nodes having a first intrinsic property within theencapsulation material, and a second layer of the multilayer PBGstructure includes a second matrix of periodically spaced nodes having asecond intrinsic property within the encapsulation material, and theencapsulation material has a third intrinsic property, and the firstintrinsic property is different from the second intrinsic property anddifferent from the third intrinsic property.
 7. The device of claim 1,wherein the photonic structure is a photonic resonant structure having apass band that includes a frequency of the electromagnetic signal. 8.The device of claim 1, wherein a frequency of the electromagnetic signalis an optical frequency.
 9. The device of claim 1, wherein a frequencyof the electromagnetic signal is a radio frequency.
 10. The device ofclaim 1, wherein the second IC die is spaced apart from the first IC dieby a separation distance that exceeds a voltage breakdown distance. 11.The device of claim 1, wherein the photonic structure includes a matrixof periodically spaced nodes within the encapsulation material, theencapsulation material has a first intrinsic property, and the nodeshave a second intrinsic property that is different from the firstintrinsic property.
 12. The device of claim 11, wherein the nodes have apermittivity that is greater than a permittivity of the encapsulationmaterial.
 13. The device of claim 1, wherein the photonic structureincludes a diffusion of particles within the encapsulation material, theencapsulation material has a first intrinsic property, and the nodeshave a second intrinsic property that is different from the firstintrinsic property.
 14. The device of claim 1, wherein the photonicwaveguide has a rectangular cross section in which a long side of thecross section is twice as long as a short side of the cross section. 15.A method, comprising: forming a photonic structure including a photonicwaveguide; through a portion of the photonic structure, attaching afirst integrated circuit (IC) die having an electromagnetic transmitterto a first die attach pad of a leadframe, the portion of the photonicstructure being located between the first IC die and the first dieattach pad; attaching a second IC die having an electromagnetic receiverto a second die attach pad of the leadframe, in which the first dieattach pad is separated from the second die attach pad, the first IC dieis spaced apart from the second IC die, and the photonic waveguide iscoupled between an output of the electromagnetic transmitter and aninput of the electromagnetic receiver; and with an encapsulationmaterial, encapsulating the first IC die, the second IC die and thephotonic waveguide.
 16. The method of Claim 15, wherein forming thephotonic structure comprises forming a matrix of periodically spacednodes within the encapsulating material, in which the encapsulationmaterial has a first intrinsic property, and the nodes have a secondintrinsic property that is different from the first intrinsic property.17. The method of Claim 15, wherein forming the photonic structurecomprises: forming a first matrix of periodically spaced nodes withinthe encapsulating material, the first matrix having a first latticeconstant; and forming a second matrix of periodically spaced nodeswithin the encapsulating material, the second matrix having a secondlattice constant.
 18. The method of Claim 15, wherein forming thephotonic structure comprises diffusing particles within theencapsulating material, in which the encapsulation material has a firstintrinsic property, and the particles have a second intrinsic propertythat is different from the first intrinsic property.